The invention relates to method and apparatus for optically measuring certain marine conditions.
Fisheries and research scientists require continuous information on the marine food chain which dominantly consists of (1) phytoplankton (typically 1 to 10 .mu.m in diameter), (2) zooplankton (typically 0.4 to 20 mm in diameter) and (3) fish, where each becomes a food source for the next in ascending order. Phytoplankton and zooplankton are measured in the oceans and studied for their interrelationships and for their profound effect on fisheries. Information is required on their abundance and vertical and horizontal distributions in continental shelf waters, deep oceans and inland waters. Acquiring this data accurately, continuously and with wide spatial coverage with limited shiptime is a major sampling problem.
In the past the sampling of zooplankton has generally been accomplished by towing large plankton nets with a mouth opening of approximately 0.5-2.0 meters and lengths of approximately 3-6 meters. Sampling phytoplankton has generally been accomplished by lowering or towing electronic instruments such as a fluorometer or a light attenuance meter. The latter instrument is less accurate in measuring phytoplankton biomass than the former but does provide an accurate vertical profile of relative concentration.
Deployment of zooplankton sampler nets from ships is generally cumbersome, time consuming and provides limited spatial coverage. The nets clog with algae material and must be recovered after short tows of approximately 10 mins. Vertical information is generally lost, since all the sample is integrated in the net, although there are two designs of multiple stacked nets which can yield improved but still limited vertical information. Obtaining simultaneous data on zooplankton and phytoplankton is often not done, since it requires the addition of other instruments thereby increasing complexity and cost. Usually the solution is to take water bottle samples on station and measure the phytoplankton biomass (using fluorometric techniques) on deck.